Create Python Add-In and Get List of Edited Features

I want to create a Python Add-In Extension that will look at the layer that is currently being edited, and as well at the features that are being edited. I'm seeing from Esri documentation that they are two properties that seem to correspond to what I'm looking for as currentLayer and editSelection (Extension class—Help | ArcGIS Desktop).

I've tried to get info using self.currentLayer or self.editSelection inside any functions such as onChangeFeature(self), onSaveEdits(self), onStartOperation(self), etc. However, self.currentLayer always return None, and self.editSelection is always empty (even if some features have been edited).

Does someone knows how to use currentLayer and editSelection properties?